The downscaling of the physical dimensions of metal oxide semiconductor field effect transistors (MOSFETs) has led to performance improvements of integrated circuits and an increase in the number of transistors per chip. Multiple gate MOSFET structures, such as FinFETs and tri-gate structures, have been proposed as promising candidates for 7 nm technology nodes and beyond. In addition, high-mobility channel materials, such as Germanium (Ge), have been proposed as technology boosters to further improve MOSFET scaling improvements.
For example, a FinFET is a multi-gate structure that includes a conducting channel formed in a vertical fin, such as a Silicon-germanium (SiGe) fin, that forms the gate of the device. Fins are typically formed in FinFETs by patterning the fin structures using direct etching of the layer of material that is to form the fin channel. High Ge content (HGC) SiGe fins are an attractive channel candidate for sub-7 nm CMOS (Complementary metal-oxide-semiconductor) technology due to higher hole and electron mobilities than with standard Si fins.
A number of techniques have been proposed or suggested for achieving high Ge content SiGe fins, such as growth of high Ge SiGe shells on Si or low Ge content SiGe fins followed by removal of the core fin. See, for example, P. Hashemi et al., “High-Mobility High Ge-Content Si1-xGex-OI PMOS FinFETs with Fins Formed Using 3D Germanium Condensation with Ge Fraction up to x˜0.7, Scaled EOT˜8.5 Å and ˜10 nm Fin Width,” 2015 Symposium on VLSI Technology Digest of Technical Papers (June 2015). While this approach works on fins along a <100> direction, where all sidewalls are on (100) planes, an epitaxial facet problem is the real issue for those fins made using a standard state-of-the-art CMOS direction, which is <110> where the fin sidewalls are on (110) planes. As a result, removal of the core results in fin instability and an unusual shape, which is unfavorable for mass production.
Thus, a need remains for improved methods for forming high Ge content SiGe fins.